(i) Field of the Invention
This invention relates to a process for the preparation of flour-like solids and fructooligosaccharides-rich flour-like solids from inulin derived from tubers of Jerusalem artichoke, and similar plants.
(ii) Description of the Prior Art
Inulin occurs as a starch-like carbohydrate in the roots of members of the family Compositae, especially Jerusalem artichoke. Jerusalem artichoke (Helianthus tuberosus), a native plant of Canada, grows well in northern climates and its tubers can yield per area greater amounts of carbohydrates than wheat or corn. Major carbohydrates in the Jerusalem artichoke tubers are fructose polymers (fructans) which consist of one terminal glucose and 2 to 35 fructose units (abbreviated GF2-35).
Inulin (high molecular weight fructans) has heretofore been isolated as a white amorphous hygroscopic powder having a specific gravity of about 1.35. It is less soluble in cold water than in hot water. It decomposes to caramel when heated to about 178.degree. C. or higher, or when boiled with alkali. Furthermore, it hydrolyzes to fructose when heated with dilute acids.
The fructan-rich tubers are normally harvested in fall or in spring after wintering in the ground. A hectare of the Jerusalem artichoke field produces about 40 to about 50 tons of the tubers or about 6 to about 10 tons of the fructans. The present cost of the tubers production is estimated to be about $55 (Canadian)/ton. Although the technology has been developed for cultivation and harvesting of the Jerusalem artichoke tubers and improvement of the tuber quality, the tubers are currently being produced only on a small scale for use as a vegetable in raw or cooked forms. However, the tubers have commercial potential to produce the several commercially-interesting products.
One product that may be produced is fructose. Fructose is at least about 1.3 times sweeter and also less cariogenic than sucrose. The ingestion of normal amounts of fructose by man does not require insulin, or stimulate the release of insulin, unlike glucose or glucose-releasing sweeteners (e.g. sucrose). Thus, fructose is suitable for consumption by diabetics and calorie-conscious people who can enjoy the same sweetness with about 30% less calories. Furthermore, fructose crystallizes less rapidly than sucrose (thus giving a smoother texture in high sugar foods); chelates metal ions (responsible for off-flavor); and enhances the inherent aroma of fruit and vegetable foods.
At present, a glucose syrup of about 55% fructose content is commonly used in food products, including soft drinks (carbonated beverages). Such syrup is generally produced from corn starch via elaborate and lengthy processes: saccharification of starch by .alpha.-amylase and glucoamylase; enzymic transformation of glucose to about 42% fructose; chromatographic enrichment to about 95% fructose; and blending of the two to produce about 55% fructose. In comparison, production of high fructose syrup from the fructans in the Jerusalem artichoke tubers would be simpler as hydrolysis of the fructans produces a syrup containing up to about 80% fructose.
In fact, U.S. Pat. No. 4,613,377 issued September 23, 1986 to H. Yamazaki and K. Matsumoto provides novel, highly useful, sweet syrups consisting of fructose and various amounts of fructooligosaccharides by the partial or substantially complete hydrolysis of fructans. The process includes first providing an aqueous solution containing inulin from Jerusalem artichoke tubers or chicory roots. Then a warm aqueous solution of fructans is passed through a column of a strong acid cation-exchange resin (proton form), thereby providing an effluent having a pH of about 2.0 to about 3.0. The effluent is then hydrolyzed by heating at a temperature of about 70.degree. C. to about 100.degree. C., and the hydrolyzate is passed through a column of an anion-exchange resin, thereby providing an effluent having a pH of about 6.5 to about 7.0. Optionally, after the hydrolysis step, the hydrolyzate is decolorized by contact with activated or granular charcoal. The effluent is then concentrated to a syrup containing less water than the effluent, e.g. one containing about 40 to about 70% solids.
Another useful product is fructooligosaccharides. Recent Japanese studies show that small size fructooligosaccharides, e.g. GF.sub.2-4 or F2-4, though not utilized by humans and animals, selectively stimulate growth of "beneficial" bacteria (bifido-bacteria in humans) in the lower intestine. When the bifidobacteria utilize these carbon sources, acetic and lactic acids are produced, thereby making the intestine environment more acidic. At such an acidic pH, the acids (particularly acetic acid) inhibit growth of "unfavorable" intestinal bacteria e.g. Escherichia coli and Clostridium perfingens which produce toxic, malodorous smelling substances, e.g. ammonia, amines, hydrogen sulfide, skatole and indole. Amines contribute to high blood pressure and can also react with nitrites to form carcinogenic nitrosamines. These unfavorable bacteria also possess high activity of .beta.-glucuronidase which regenerates toxic or carcinogenic substances from their .beta.-glucuronides, detoxification products from the liver. The acids (generated by bifidobacteria) retard not only the growth of these bacteria but also intestinal absorption of ammonia and amines by protonation and stimulate bowel movement. Bifidobacteria provide the hosts with vitamins (B1, B6, B12, pantothenic and nicotinic acids), degrade nitrosamines, and stimulate intestinal immunity against infection. Decline of the bifidobacteria population is commonly observed in unhealthy or elderly humans. Clinical studies have shown that oral administration of fructooligosaccharides increases the biofidobacteria population in the lower intestinal tract; reduces the population of "unfavorable" bacteria; and reduces constipation, blood lipids in hyperlipidemia, blood pressure, blood cholesterol and production of intestinal toxic substances. Fructooligosaccharides exist in many plants e.g. onion, asparagus, rye and banana but at relatively low levels.
Meiji Seika Ltd. of Japan has commercialized fructooligosaccharides production from sucrose by the action of Aspergillus niger .beta.-fructofuranosidase (GF.fwdarw.GF2+GF3+GF4, etc.). Fructooligosaccharides are now widely used as an ingredient in food (drinks, confectionaries, preserves, dairy products, etc.) in Japan. As a feed ingredient, fructooligosaccharides have been used to reduce diarrhea, to improve weight gain and feed efficiency in piglets after weaning and also to reduce fecal odour of pets.
The process used by Meiji Seika to prepare fructooligosaccharides yields a large amount of glucose (e.g. about 50%) in addition to fructooligosaccharides. Removal of glucose is necessary to prepare dry powder or glucose-free products, which requires a relatively expensive chromatographic process. On the other hand, it is possible to prepare dry powder (which contains greater than about 50% fructooligo-saccharides) by partially hydrolyzing the Jerusalem artichoke fructans either with acid or with endo inulinase. Furthermore, a major monosaccharide generated from the Jerusalem artichoke fructans is fructose rather than glucose.
A major problem in commercialization of the Jerusalem artichoke tuber products is that the fresh tubers are available for only about 3 to about 4 months in a year. A year-round production requires the storage of the tubers. Although mechanical refrigeration and proprietary "liquid storage" techniques are effective in storing the tubers, the methods are expensive in terms of capital and the requirement of space and transport of the tubers into and out of storage. Although dehydration of the tuber slices permits inexpensive storage, the dehydration process proposed heretofore is slow and expensive. Furthermore, the extraction of the fructans from the dried slices requires either rehydration or energy-intensive grinding, and the recovery of the fructans is far from complete (e.g. about 50%). At present, there is no rapid and economic method for processing a larger amount of the tubers to avoid the high cost of storage.
It has been observed that many people who regularly eat Jerusalem artichoke tubers as a vegetable benefit from similar effects as observed with fructooligosaccharides. However, these benefits are not available all year round because of difficulty in storing the tubers economically. These effects should increase when the fructans are converted to smaller fructooligosaccharides which are more efficiently utilized by bifidobacteria.
It is known that the solids (about 20% of the tuber weight) in the Jerusalem artichoke tubers consist of about 60 to about 80% fructans; about 8 to about 12% proteins; about 4 to about 6% fibre; and about 4 to about 8% ash rich in potassium.
It is therefore desirable to provide Jerusalem artichoke in the form of a flour-like solid, having substantially the same content of fructans, proteins, fibre and ash as aforesaid. Unlike the tubers, the flour-like solid would be readily available to consumers throughout the year and should find greater food applications (e.g. baked foods, e.g. bread and pizza crust). Unlike the syrup, the flour-like solid can be used in dry formulations and is easier to dispense. The flour-like solid would be an ideal source of low calorie food. For diabetics, obese or elderly people, the fructooligosaccharides-rich flour-like solid is an ideal food ingredient. For pets, the fructooligosaccharides-rich flour-like solid can be added to their foods to control fecal odour and maintain health, as fructooligosaccharides also reduces production of putrefactive substances in the intestine of the pet. For piglets, the flour-like solid can be added to the milk replacer to reduce diarrheas of bacterial origin.
Jerusalem artichoke flour-like solid is currently produced on an experimental basis by drying the sliced tubers at 50.degree.-80.degree. C. for several hours and "hammer" milling the dried (hardened) slices. This method is slow and energy intensive, and may also generate undesirable color and off-flavor partly due to the oxidation of tuber phenolic acids by polyphenol oxidase.
Canadian Patent No. 358,340 issued June 9, 1936 by J. W. Reavell provided a process for producing fruit and vegetable products. The patented process involved subjecting pulp of a predetermined consistency and derived from whole fruit or vegetables, subjected to a certain preliminary treatment, to a spray drying operation under carefully regulated conditions. The preliminary treatment involved subjecting the whole fruit or vegetable to a mincing, crushing or chopping operation to provide a pulp. The pulp was then further subjected to two or more treatments through disintegrating machines or mills to reduce the pulp to a finely divided condition. The cold, finely divided pulp was passed or pumped to a spraying or atomising apparatus wherein the spray produced was brought into direct contact with a heated aeriform or gaseous medium where it was heated for the first time to evaporate the moisture, and to provide a powdered fruit or vegetable product.
Marchand U.S. Pat. No. 2,555,356 related to a method for the preparation of inulin. Previous procedures for producing inulin are also described therein, which generally involved extracting ground dry Jerusalem artichoke tubers with hot water. The patented process involved centrifugal clarification of the syrupy juice pressed from ground Jerusalem artichoke tubers. Dry powder was produced by crystallization from acetone.
Hill U.S. Pat. No. 2,834,694 patented May 13, 1958 provided a process for preparing fructose polymers from inulin or inulin-containing plants. The patented process involved first extracting slices of the inulin-containing plant with an organic extraction solvent. The residual inulin in the extracted slices was then extracted with warm water followed by precipitation of the inulin. Then the inulin was hydrolyzed with heat in the presence of a weak acid.
It is known that Jerusalem artichoke tubers contain polyphenols and active polyphenol oxidases which catalyze the oxidation of the polyphenols to the corresponding quinones in the presence of oxygen. The resulting reactive quinones couple with amino acids and proteins, generating brown coloration (discoloration).
In the past, it was suggested that such discoloration could be prevented by passage of sulfur dioxide or by the addition of sodium metabisulfite to a macerate of Jerusalem artichoke tubers. While this technique is suitable to prevent discoloration, such added compounds generate off-flavors in products, corrosion in equipment and their use is prohibited in some countries.
It was also suggested that such discoloration could be prevented by the addition of ascorbic acid, which prevents discoloration by reducing the quinones. However, this technique is not suitable because relatively large amounts of ascorbic acid are required, thus increasing the cost of production.